1. Field of the Invention
The invention relates to catheters, and more particularly, to long-term indwelling catheters, used in the central venous system of a patient, for controlling patient body temperature.
2. Description of Related Art
Catheters such as central venous line catheters are typically used in ICU (intensive care unit) patients, particularly in those patients who have suffered a stroke or other brain traumatic event. The central venous line catheters are typically about 5.0-12 French in size and consist of a soft, flexible multi-lumen structure extending 6-12 inches. They are usually introduced through the subclavian or jugular vein, and less preferably in the femoral vein of the patient, serving to provide the caretaker with easy and convenient access to the patient""s central blood supply via the central venous system. In this manner general access to the central blood supply is gained, enabling for example delivery of drugs, infusion fluids or nutrition, along with the gathering of patient blood for blood gas analysis, measurement of blood pressure, and the like.
In many patients, such as ICU patients, fever is a common occurrence. Fever is particularly likely in neuro-ICU patients, and its onset can exacerbate detrimental effects in the brain. Conventional therapies to control fever include treatment with acetaminophen (Tylenol), cooling blankets, ice water bladder lavages, and ice baths. All of these approaches to cooling a patient require excessive time to cool the patient. Moreover, prior methods do not provide for precise control of patient cooling. As recognized herein, to optimize the advantage of cooling a patient, it is important to cool the patient relatively quickly in a controlled fashion.
Indwelling catheters are known that can be implanted in the body of a patient to remove heat from the blood supply of the patient, thereby in turn reducing the patient""s core body temperature. A known indwelling catheter is disposed in a heat exchange relationship with the blood supply, and a heat exchange fluid is circulated through a set of lumens and an inflatable balloon in a closed loop. The heat exchange fluid flowing in the balloon exchanges heat with blood flowing past the balloon, lowering the temperature of body tissue and, as mentioned above, thereby improving the patient""s medical outcome.
The advantages of the above-referenced cooling catheter can be implemented into a central venous catheter configuration. As mentioned above, central venous catheters are commonly used in many ICU patients, including neuro-ICU patients, and it would be advantageous to provide a central venous catheter with the capability of cooling a patient effectively.
Heat transfer capacity of known cooling catheters is believed to be limited, because of two fluid dynamic actions. First, it appears that the cooling fluid flowing in the balloon separates into laminar layers, with a first layer flowing in a long path past the inner surface of the balloon, and one or more additional layers beneath the first layer, flowing in a shorter path along the axis of the catheter. The fluid in the lower additional layers does not flow adjacent to the blood, and does not exchange heat with the blood. Only the outer layer flowing past the inner surface of the balloon exchanges heat with blood outside the balloon, so not all of the cooling capacity of the fluid is utilized. Second, it appears that blood flowing in the vein also separates into laminar layers, with a first layer flowing past the outer balloon surface, and other layers above the first layer flowing past the vein""s inner wall. Only the layer flowing past the balloon""s outer surface is exposed to the cooling effect of the catheter, so not all of the blood is available to be cooled, again adversely affecting the catheter""s heat exchange capacity.
The present invention obviates one or more shortcomings of the prior art by providing a central venous line catheter adapted to actively exchange heat with the body of the patient to thereby raise or lower the patient""s body temperature as required. The central venous line is provided with a heat exchange element disposed in heat exchange relationship with the blood of the patient. The heat exchange element houses a circulating fluid therein, with the fluid being automatically cooled or warmed exteriorly of the patient""s body in accordance with a patient temperature feedback scheme. The heat exchange element includes an inflatable balloon having a spiral configuration, which causes laminar layers of cooling fluid flowing in the balloon to mix together.
By supplementing the known functions of a central venous line catheter with the function of cooling or warming the patient""s blood, the present invention takes advantage of existing access to the venous system and a single, relatively small incision, reducing the risk of additional complications. The access, typically through the subclavian, jugular or femoral veins, is to the central blood supply, via the central venous system, and is therefore particularly expedient, permitting efficient cooling or warming of patient body temperature. The term central venous system generally relates to the portion of the venous system which returns blood to the right side of the heart, including the inferior and superior vena cava. A particular advantage of the invention is that the cooling function is performed efficiently in tandem with a procedure which is known to be likely attended by fever, thus anticipating such fever and facilitating its control. The heat exchange relationship between the system and the central venous system of the patient can be maintained for a prolonged durationxe2x80x94for example, from about one hour to about twenty-nine days. Moreover, because cooling fluid flow layers in the spiral balloon are mixed, cooling capacity of the system is increased over that of known cooling balloon catheters.
The central venous line catheter in accordance with the invention comprises a tubular structure defining a plurality of lumens. At least two of these lumens convey heat exchange fluid to and from a heat exchange element disposed at a distal, implantable end of the central venous line catheter, while the rest of the lumens may be used to provide access to the central blood supply of the patient. The heat exchange element is in fluid communication with a temperature control module via a tubing set which conveys the heat exchange fluid between the components. The temperature control unit comprising a cooling and/or a heating device, operates in conjunction with a temperature controller to heat or cool the heat exchange fluid depending on a sensed temperature of the patient. The heat exchange element includes at least one expandable balloon having a spiral shape.
The system of the invention operates to maintain patient temperature at a desired level. Any deviation from the desired level automatically triggers corrective action, such as circulating cooled heat exchange fluid through the central venous line catheter to contend with the onset of fever. Additionally, the system is equipped with indicators which signal to the caretaker of the patient the sensed deviation, by for example sensing the increased workload of the system, in order to warn of adverse physiological changes besetting the patient, such as infection.
The invention thus provides a system controlling patient temperature using a central venous line catheter having a heat exchange element. The central venous line catheter is provided with one or more lumens, preferably for providing access to the central blood supply of the patient, and with additional lumens for communicating heat exchange fluid to the heat exchange element. Heat exchange fluid temperature is controlled through a feedback loop in which patient temperature is sensed and used to control a temperature control unit comprising a heating device and/or a cooling device in heat exchange relationship with the heat exchange fluid. A tubing set transports the heat exchange fluid between the central venous line and the temperature control unit, with a pump serving to circulate the fluid in a closed fluid circuit in the system. The heat exchange element has a spiral shape to promote mixing of the heat exchange fluid flowing in the element.